This synthesis should be performed in the hood. Potassium cyanide hydrolyzes under appropriate conditions to generate hydrogen cyanide.
The dark-red solution obtained on dissolving 6.0 g. (0.030 mole) of 1,10-phenanthroline monohydrate together with 3.9 g. (0.010 mole) of ferrous
ammonium sulfate hexahydrate in 400 ml. of water is heated to just below the boiling point. A freshly prepared solution of 10 g. of potassium cyanide
in 20 ml. of
water is added all at once to the hot solution. After thorough stirring, the hot mixture is set aside to cool at room temperature. Dark violet, almost
black, dense, fine crystals develop rapidly. Precipitation is complete within several minutes; however, an aging period of an hour or longer is
considered beneficial. The yield of crude product, after filtration and generous washing with water, is approximately 5 g. The filtrate contains about
2 g. of free 1,10-phenanthroline that can be recovered by extraction with either benzene or diethyl ether.
For purification, the crude product is dissolved in 30 ml. of concentrated sulfuric acid. To the vigorously stirred solution 1 l. of water is slowly
added. The recrystallized product is collected by suction filtration and washed thoroughly with small portions of water until free of sulfuric acid. A
final rinse with acetone facilitates drying. The product is vacuum-dried at room temperature. The final yield ranges from 4.0 to 4.9 g. (80-98% based
on the iron(II) salt). |
